Worked fine until today (31/05/2012).
When choosing a February date set to March (
Similarly, if you choose to September - is chosen in August, with the remaining months, everything is OK, what could be the reason?

error on the 31st

This problem can be easily replicated: 1. Change the date on your computer's "Time and Date Settings" to May 31 or any31st day of a month. 2. Close the browser entirely and reopen it. It gets its date setting when thebrowser program starts up, so reopen it to trick the date.3. That's it. You were onto it with the 31st and 30 days in a month problem. Essentially thedatepicker is trying to put that month onto the same day as 'today'...so if youdo it on the 31st, it's hidden day value is a 31 and thus the problem with 30day months. (Or February on the 29th) It occurs on 'blur' because that's when the form field validates itself andrealizes that it's showing a June12 but it's internal value is actuallyJuly1,2012...because there is no June 31...so it corrects itself.